50 million people, $6 billion … and one tree

On Thursday, Aug. 14, 2003, a massive power outage began on the New York state power grid shortly after 4 p.m. It would cascade to become the most widespread blackout in North American history. At its peak, it affected 50 million people across much of the northeastern United States and most of southern Ontario.

Aug. 13, 2003
(the preceding day)

9:03 pm, Aug. 14, 2003
(the height of the blackout)

The power was off until late that evening for some people, and many did not get their power restored until the next morning.

Eleven people died, and the estimated economic impact of the outage was $6 billion.

It all started when a single tree came into contact with a transmission line in Ohio, triggering a cascade of events that within two hours blacked out millions of homes and thousands of businesses, paralyzing rush hour traffic and shutting down fans and air conditioners
on one of the hottest days of the year.

This event came to be known as the Northeast Blackout, and it was the largest in U.S. history. It shows how easily the wrong tree in the wrong place can set off an avalanche of transmission system failures that can produce catastrophic consequences hundreds of miles away.